1. Field of the Invention
The present invention relates to a new and improved twin wire former for the manufacture of paper or the like.
Generally speaking, the twin wire former of the present development for the manufacture of paper or the like is of the type comprising two co-running endless revolving forming wires which converge towards or merge with one another to conjointly form therebetween a fiber stock inlet gap or wedge opening. In this condition the forming wires are conjointly guided along a web or sheet forming zone. One of the forming wires defines a transport wire and the other forming wire defines a counter wire. Additionally, there is provided at least one forming roller about the circumference of which there are at least partially conjointly trained or wrapped both of the endless revolving forming wires. As viewed in a predetermined direction of travel of the forming wires at least one stationary forming element is arranged forwardly or upstream of the forming roller in a first forming section at one side of the two forming wires and bears against at least one of the forming wires.
2. Discussion of the Background and Material Information
Such type twin wire former has been disclosed in the German Published Patent Application No. 3,815,470, published Nov. 16, 1989. In such twin wire former there are incorporated forming shoes, forming rollers and support surfaces which are intended to guide a first forming wire or a second forming wire. The shear load between the forming wires exerted upon the fiber stock suspension is weak, and that is the reason that such twin wire former must be operated with an appreciable amount of dilution water. When fabricating packaging paper have a weight in the range of 100 g/m.sup.2 to 280 g/m.sup.2 this results in a large structural height of the former which can exceed 8 meters and requires a greater length for the formation of the sheet or web formed from the fiber stock. In this twin wire former during the formation of the web, the web forming process is completed at a point E (FIG. 2) of the wrap length of the forming roller. Thereafter, there is still carried out dewatering at a support surface and a suction roller.
On the other hand, when fabricating packaging paper there are increasingly attained, with so-called Intensa presses, greater operating velocities exceeding 1000 m/min. In this regard and as can be gleaned from the European Published Patent Application No. 0,289,445, published Nov. 2, 1988, considerable difficulties are encountered in the removal of water, especially in a direction opposite to the direction of the force of gravity. The forming wire water cannot be directly removed perpendicular to the forming wire at the site where it is formed. Rather, such forming wire water first must be collected at guide surfaces and suctionally removed by vacuum. As a result, contaminants are produced, particularly an undesired stock-mist formation.
In the solution proposed in U.S. Pat. No. 4,790,909, granted Dec. 13, 1988, there is strived to obtain symmetrical dewatering of the web or sheet. However, since the forming shoes are arranged in offset configuration, the dewatering towards the outside differs with time and is of different intensity, resulting in an irregular formation structure of both sides of the paper web or sheet. Additionally, the equipment has a very large structural height, leading to vibrations of parts of the equipment or machine, and thus, impairs the quality of the fabricated paper. In particular, at especially high machine velocities the turbulence of the stock suspension produced by the stationary dewatering elements is impermissibly increased and there is marred the web or sheet formation.